In the last 20 years, the role of subcortical structures in brain functioning has become a major field of research. In particular the role of the striatum in executive functions (attention, planning, and working memory) is becoming increasingly understood. However, despite the advent of new brain imaging techniques, its role in language remains a controversial and an unresolved issue, presumably because of technical limitations and because animal models cannot be of any help. Evidence in humans come from language impairments reported for vascular subcortical damage and for neurodegenerative diseases of the basal ganglia, such as Huntington’s disease (HD), which primary targets the striatum at the early stages. Impairments observed in these studies encompass a large range of deficits from various aphasic profiles to isolated dysarthria, disorganisation of semantic knowledge in vascular disorders, or syntactic impairments in HD. Most of these observations are not driven by specific hypotheses on language processing and do not allow one to understand the specific role of the striatum in the broader frame of the language processing. In contrast studies conducted by Ullman 1997 suggest that patients suffering from HD are specifically impaired in syntax processing, which in turn suggest that syntax processing is located in a fronto-striatal circuit. However, although some rules (like morphological conjugation rules or syntactic movement rules) are impaired, canonical structure or pragmatic strategy remain spared (Teichamnn et al., 2005). Thus, studying these patients allow to disentangle various theories of language and their link with other cognitive function like memory or executive functions. Thus, the characterisation of the language disorders accompanying striatal dysfunction and its neural basis, which may reflect either subcortical damage or concomitant cortical dysfunction, constitutes a major challenge for the understanding of language processing.
This lecture will present the state of the art in this line of investigation, some ongoing research and some speculations regarding what it shows regarding the neural substrates of the language faculty.